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It Prints nothing from the ArrayList?

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It Prints nothing from the ArrayList?

 
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  #1
May 24th, 2009
Java Syntax (Toggle Plain Text) 
  1.  
  2.  
  3.  
  4. import java.io.*;
  5. import java.util.*;
  6.  
  7. public class MainTwo {
  8. public static void main(String[] args) {
  9.         for(File file : File.listRoots()){ 
  10.             search(file);
  11.         }
  12.     }
  13.  
  14.     public static void search(File f) 
  15.     {  
  16.         ArrayList<File> arrayList = new ArrayList<File>();
  17.             f.listFiles();
  18.             arrayList.add(f);
  19.  
  20.             System.out.println (f.getName());
  21.  
  22.  
  23.     }
  24. }

Why does it print nothing?
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Re: It Prints nothing from the ArrayList?

 
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  #2
May 24th, 2009
i just tried a differrent approach, this code also prints out nothing


Java Syntax (Toggle Plain Text) 
  1.  
  2.  
  3.  
  4.  
  5. import java.io.*;
  6. import java.util.*;
  7.  
  8. public class MainTwo 
  9. {
  10.     public static void main(String[] args) 
  11.     {
  12.         File[] filesOnComputer = File.listRoots(); 
  13.         {
  14.             ArrayList<File> listOfFiles = new ArrayList<File>();
  15.             for(int index = 0; index < filesOnComputer.length; index++)
  16.             {
  17.                 listOfFiles.add(filesOnComputer[index]);    
  18.                 System.out.println (filesOnComputer[index].getName());
  19.             }
  20.         }
  21.     }
  22. }

why does it print out nothing??
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Re: It Prints nothing from the ArrayList?

 
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  #3
May 24th, 2009
Do you mean prints nothing, or just "c:"? Because your code just seems to print the results of the listRoots. You do call listFiles, but you do nothing with it.
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Re: It Prints nothing from the ArrayList?

 
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  #4
May 24th, 2009
i see two issues:
1) First u r calling listRoots, tht must print C:\
2) Secondly, u r not trying to get the iterate through the list of files that u got...

Let see ur code:
File[] filesOnComputer = File.listRoots();

this part shall give u the root of the directory structure (in most cases it would be C:, in case it is partioned it might also give D

then u will have to chk whether this is a directory, and if it is then u will have to call ur search function with little modification as:

public static void search(File f)
{
ArrayList arrayList = new ArrayList();
File[] files= f.listFiles(); // get all files under the direcrory
for(int index = 0; index < files.length; index++)
{
System.out.println ("here we are---"+files[index].getName());

arrayList.add(files[index].getName());
}
System.out.println (f.getName());


}

u might need to also call this recursively to see if the next selection is a file or a directory.

Try this :

public static void main(String[] args)
{
File[] filesOnComputer = File.listRoots();
{
ArrayList listOfFiles = new ArrayList();
System.out.println (filesOnComputer.length);

for(int index = 0; index < filesOnComputer.length; index++)
{
listOfFiles.add((File)filesOnComputer[index]);
if(filesOnComputer[index].isDirectory()){
System.out.println ("here we are-"+filesOnComputer[index].getPath());
search((File)listOfFiles.get(index));
}
else
System.out.println ("This is not the directory-"+filesOnComputer[index].getPath());
}
}
}
public static void search(File f)
{
ArrayList arrayList = new ArrayList();
File[] files= f.listFiles();
for(int index = 0; index < files.length; index++)
{
System.out.println ("here we are---"+files[index].getName());

arrayList.add(files[index].getName());
}
System.out.println (f.getName());


}
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Re: It Prints nothing from the ArrayList?

 
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  #5
May 24th, 2009
wow nicely explained thanks are you a teacher?

yep next step recurssion
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Re: It Prints nothing from the ArrayList?

 
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  #6
May 25th, 2009
Rather than the pre-1.5 old-style for loops and un-typed lists, replace

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ArrayList arrayList = new ArrayList();
File[] files= f.listFiles(); // get all files under the direcrory
for(int index = 0; index < files.length; index++)
{
System.out.println ("here we are---"+files[index].getName());

arrayList.add(files[index].getName());
}
with

java Syntax (Toggle Plain Text) 
  1. ArrayList arrayList<File> = new ArrayList<File>();
  2. for(File ff : f.listFiles()) {
  3.   System.out.println ("here we are---"+ff.getName());
  4.   arrayList.add(ff.getName());
  5. }
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Re: It Prints nothing from the ArrayList?

 
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  #7
May 25th, 2009
i got the recursion working, couldnt quite implent the new for loop, moved on to the next step, ei. trying to compare files in two ArrayLists, and the first hiccup is as follows:

Java Syntax (Toggle Plain Text) 
  1.  
  2.  
  3.  ArrayList arrayList = new ArrayList();
  4.             ArrayList arrayListAgain = new ArrayList();
  5.  
  6.             File[] files= f.listFiles();    
  7.             for(int index = 0; index < files.length; index++)
  8.  
  9.             if (files[index].isFile())
  10.             {
  11.  
  12.                 System.out.println ("here we are---"+files[index].getName());
  13.  
  14.                 arrayList.add(files[index]);
  15.                 arrayListAgain.add(files[index]);
  16.  
  17.                 if (arrayList(files[index]).length() == arrayListAgain(files[index]).length() && arrayList(files[index]).hashCode() != arrayListAgain(files[index]).hashCode())
  18.                 {
  19.                     //do something;
  20.                 }
  21.             }


Hmm my compiler friend tells me cannot find symbol - method arrayList(Java.io.File)??

The java class library for ArrayList was not helpful to me.
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Re: It Prints nothing from the ArrayList?

 
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  #8
May 25th, 2009
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Originally Posted by caps_lock View Post
i got the recursion working, couldnt quite implent the new for loop, moved on to the next step, ei. trying to compare files in two ArrayLists, and the first hiccup is as follows:

Java Syntax (Toggle Plain Text) 
  1.  
  2.  
  3.  ArrayList arrayList = new ArrayList();
  4.             ArrayList arrayListAgain = new ArrayList();
  5.  
  6.             File[] files= f.listFiles();    
  7.             for(int index = 0; index < files.length; index++)
  8.  
  9.             if (files[index].isFile())
  10.             {
  11.  
  12.                 System.out.println ("here we are---"+files[index].getName());
  13.  
  14.                 arrayList.add(files[index]);
  15.                 arrayListAgain.add(files[index]);
  16.  
  17.                 if (arrayList(files[index]).length() == arrayListAgain(files[index]).length() && arrayList(files[index]).hashCode() != arrayListAgain(files[index]).hashCode())
  18.                 {
  19.                     //do something;
  20.                 }
  21.             }


Hmm my compiler friend tells me cannot find symbol - method arrayList(Java.io.File)??

The java class library for ArrayList was not helpful to me.
maybe you mean something like this?
Java Syntax (Toggle Plain Text) 
  1. ArrayList<File> arrayList = new ArrayList<File>();
  2.     ArrayList<File> arrayListAgain = new ArrayList<File>();
  3.  
  4.     File[] files= f.listFiles();    
  5.     for(int index = 0; index < files.length; index++)
  6.  
  7.     if (files[index].isFile())
  8.     {
  9.  
  10.         System.out.println ("here we are---" + files[index].getName());
  11.  
  12.         arrayList.add(files[index]);
  13.         arrayListAgain.add(files[index]);
  14.  
  15.         if (arrayList.get(index).length() == arrayListAgain.get(index).length() && 
  16.           arrayList.get(index).hashCode() != arrayListAgain.get(index).hashCode())
  17.         {
  18.             //do something;
  19.         }
  20.     }
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Re: It Prints nothing from the ArrayList?

 
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  #9
May 25th, 2009
thanks jaka.ramdani


I tried making the modifcation you siggested, but the compiler error with that was:

cannot find symbol - method length

and then i tried using (files[index]) in the if statement, and then it said cannot find symbol - method get


so frustrating!
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Re: It Prints nothing from the ArrayList?

 
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  #10
May 25th, 2009
oh my fault i didnt make all the changes it does compile, rep for you!
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